wire break sensor alarm circuit schematic

Wire Break Sensor Alarm

Circuit of a loop sensor based simple security alarm is described here. The sensor loop is nothing but a short length of thin enamelled copper wire, which bridges two input points of the electronic alarm circuit. When the loop is opened the alarm circuit fires an active electric/electronic hooter to raise an ear-splitting audio alert signal. The circuit requires 12 volt dc supply for proper working.

When the loop is closed, anode terminal of diode D1 is at ground level and transistor T1 is off. When the loop opens, capacitor C1 is quickly charged via resistor R1 and diode D1, whereupon mosfet T1 comes on so that the hooter (BZ1) is switched on. If the loop is closed again, initial condition is maintained by grounding the anode of D1 and this stops the charging of C1. However, C1 is disharged fairly slowly via R2, so that T1 is not switched off immediately! This ensures that the alarm remains active for a little more time and then goes out slowly. This timeout can be changed by varying the value of R1,R2 and C1. Mosfet T1 may be one of many types of popular n-channel power mosfet, but it should be able to handle the selected 12V hooter of your choice.

Wire break alarm circuit schematic

wire break sensor alarm circuit schematic


Join the conversation!

Error! Please fill all fields.
  • dev

    Dear sir how will conation of the hooter ….? I have two wire In and Out

  • countrywill

    Hi could you please let me know what R1,R2 and C1 would need to be to switch the siren off immediately when loop is closed again

  • HARI

    can this be used to detect cracks in tracks,linking it with tracks instead of wire

  • priyanka ghule

    sir can u pls send me the principle, aplication, and working of this ckt so it will help me in my project report.

  • aditya

    hello reader, i have problem in addressable fire alarm.
    i.e; 1, sounders open
    2, cable break
    3, device fault
    system name is premier quatro addressable fire alarm.
    i need solution. when u have plz revert me.

    thanks and warm regards

  • Swapnil n. Rajput

    nice project . i like it

  • himanshu suthar

    Dear Sir ,
    I have an requirement of detecting a sensor cable break alarm. we have a system that sense the powder. this sensor has a simple ss metal rod . there is two cable is connected to this sensor . one cable is connect to the ss rod and another cable is connected to the sensor shield the shield is normally ground. now when the powder is sense by sensor there will be some millivolts are genrated. that volts we measure .now when this two or one cable is break .so we get the alarm so please send me any circuit for this system if it is possible.


  • Aiel

    Sir, Do you have any circuit that has unique sound which is suitable for car parking alarm? (Disregard fire alarm, police siren and any usual alarm.)

    Thank you Sir.

  • HN..


  • SkyNet

    P. Marian,
    you have same circuit in low current (3v/5v.)?

    What i do, the same circuit work in 3v.?
    I already made This circuit.


  Search 4 million + Products
Browse Products